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spectra. It was found that the line spectra was materially changed when 
the center in question was placed in a strong magnetic field. Later this 
was shown to be related to the vibration of a negative charge of small 
magnitude, giving additional confirmation of the electron theory of radiation. 
We know that when a particle or particles of matter execute some form of 
simple harmonic motion with sufficient frequency that a note of definite 
pitch is produced. Why can not we carry the sound analogy over into the 
realm of electronic motion and conceive of one of these electrons executing 
some form of simple harmonic motion with, of course, some definite period, 
its frequency bearing some definite relation to its temperature, as proposed 
by Planck. 
If the sound analogy referred to applies to combined waves of varying 
frequency and wave length so as to produce ‘“‘spectral harmonics” to coin 
such a phrase, the center producing them must of necessity be very complex. 
Take for instance the fluorescent effects noted when the vapors of certain 
metals is examined; or the luminosity of a gas when a small portion of its 
molecular aggregate has been ionized. It has been found that when 
1 mike : 
10,000,000 part of the molecules of a gas has been ionized that it becomes 
luminous. Likewise it has been observed that dissociation of some of the 
halogen group is accompanied by changes in its absorption spectrum. Many 
experiments also show that fluorescence and likewise phosphorescence are 
due to or accompanied by dissociation or ionization. 
Considerable light has been shed upon this problem by the study of the 
emission of heat by radioactive substances. Curie and Laborde found in 
1903 that the temperature of a radium compound was maintained by itself 
several degrees higher than its surroundings. It was found that radium 
emitted heat at a rate sufficient to more than melt its own weight of ice 
per hour. According to Rutherford the emission of heat from radioactive 
substances is a measure of energy of the radiation expelled from the active 
matter which are absorbed by itself and the surrounding envelope. This 
heating effect was supposed to be a measure of the kinetic energy of the 
expelled a@ particles; the heating effect was calculated by determining the 
kinetic energy of the a particles expelled from one gram of radium per 
second. 
K.E. = } mn 2V2m = mass of particle. 
I 
n no. emitted by each group per second. 
vy = the velocity of the different group of particles 
